People rely heavily on a wide variety of electrical devices. Almost all of these devices draw power ultimately from a commercial source, usually delivered to the user through a wall outlet or socket. While many electrical devices are sold for use throughout the world, there is no world standard for electrical plug configurations, size, shape, position or number of prongs. The wide variety of socket configurations in use worldwide burdens international suppliers of products to varied countries and international travellers who wish to use electrical devices in varied locations.
Most industrial nations use a standardized alternating current supply with a hot side and a neutral side. Some plugs specifically incorporate a separate earth or ground lead while others do not. While there is no world standard for power supply voltage or frequency, many electronic devices, and essentially all battery powered electrical devices, ultimately run on direct current, so it is not too difficult to design a "universal" power supply that converts 100-240 volts AC at 50-60 Hertz into a direct current suitable for a particular application. A problem remains, however, with physically accessing an AC current source supplied through any number of outlet configurations.
Differing plug configurations have posed a problem to manufacturers who sell equivalent products into various parts of the world. Plug diversity is also a significant problem for people who travel to different parts of the world and need to take electrical devices with them, particularly devices such as hair dryers, electronic cameras, phones or computers.
The traditional solution for the mechanical configuration problem is to provide an adapter which includes a socket to accommodate the prongs of the electrical device integrated with a second set of prongs in a configuration for a local socket. These adapters suffer from some significant problems. The most important is that the adapters are bulky and at a minimum cause the prongs of the original device to be extended by at least the length of the additional set of prongs. Since most plug devices are designed to be secured by spring tension and interaction with a wall plug, this can pose a significant mechanical disadvantage. The increased lever arm created by the additional prong length will tend to shift the plug downward, tending to pry the plug out of the wall socket. This will be true even for a light weight plug.
The lever arm problem is accentuated with devices that are larger than a simple plug. Many battery chargers or power supplies are designed to be wall-mounted at a wall socket. A typical device includes a casing which terminates in a plug designed to plug directly into the wall socket. The casing is often designed to lie against a wall to provide mechanical stability and to maintain the plug prongs in proper contact with the wall socket. If an adapter must be used, the unit loses the stability of resting against the wall and, because even a small amount of weight at the end of a lever arm will create a torque which will tend to pry the prongs out of the wall socket, such a plug adapter is generally unusable for such wall amounted plug-in devices.
Angling the plug severely can compromise the electrical connection to the point that the plug no longer is in electrical contact with source current. This type of angling may lead to partial separation from the wall socket and may expose the prongs of the plug in such a way that a person or animal might come into contact with live current, thereby causing bodily harm.
A further problem with existing plugs is the awkward shape of the plug with prongs protruding from the end. If, for example, a plug is moved from location to location, the prongs of the plug extend outward and can be difficult to pack or store or can catch on clothing when packed into a travel case.
A few plug devices have been designed with a plug or prongs which fold into a casing. For example, some rechargeable flashlights include the collapsible prongs which can be rotated into a position extending out from the body of the flashlight and plugged directly into a wall socket or extension cord. In another example, some telephone charging stations include a cradle for the telephone and a rotatable plug which can be extended into position for plugging into a wall socket, or collapsed into a space in the shell of the charging station, particularly so that a user may slip a charging station into a pocket, a briefcase, or other container.
Presently available collapsible plug devices suffer from various problems which make them inconvenient or even dangerous to use. In particular, the rotatable plug has only a weak spring holding the plug in position. It does not take much effort to collapse the plug, which may cause the plug to partially or completely pull out of a wall socket. This can compromise the electrical connection to the point that the plug no longer is in electrical contact with source current. In some circumstances, this may expose the prongs of the plug in such a way that a person, might come into contact with live current, thereby causing bodily harm. In addition, a collapsing plug might pinch the user.
The new device of this invention overcomes these problems by providing a plug device which can be securely maintained in the extended position but folded easily to a compact, collapsed position. This collapsible prong feature is incorporated within an interchangeable plug device which can be designed for use in a variety of plug configurations and still provide the mechanical advantages of fitting closely to the socket and, generally, against a wall. Moreover, the inventive device provides a safe means for deriving current from an interchangeable plug while minimizing the risk of exposure to a live prong or connector.